mail.skylinux.org has no MX records.
Question and response
Question
dig mail.skylinux.org. MX
Answer
The response has no answer records.
Authority
skylinux.org. 3600 SOA NS1.DOTSTER.COM. namehost\@WORLDNIC.COM. 124102721 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0